SMTPS (SMTP over SSL)
What is Port 465?
Port 465 was originally assigned for SMTPS (SMTP over implicit SSL/TLS) for secure email submission. It was briefly de-assigned and then re-assigned in RFC 8314, which recommends its use for email submission with implicit TLS. Unlike port 587 which uses STARTTLS to upgrade a plaintext connection, port 465 establishes a TLS-encrypted connection from the start. This means all communication including the initial SMTP handshake is encrypted. Major email providers including Gmail, Outlook, and Yahoo support port 465 for secure email submission from email clients. The re-standardization in RFC 8314 (2018) settled the long-standing debate about whether to use port 465 or 587, recommending both as valid options with implicit TLS on 465 being preferred for new implementations.
Common Uses
- Secure email submission from mail clients
- Application email sending with TLS encryption
- Automated notification systems requiring encrypted SMTP
- Email relay with mandatory encryption
Technical Details
Copy-paste commands to check port 465 (SMTPS (SMTP over SSL)) from your terminal
Test connectivity
nc -zv example.com 465
curl -v --max-time 5 http://example.com:465/
telnet example.com 465
nmap -p 465 -sV example.com
(echo > /dev/tcp/example.com/465) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 465/tcp
sudo iptables -A INPUT -p tcp --dport 465 -j ACCEPT
sudo firewall-cmd --permanent --add-port=465/tcp && sudo firewall-cmd --reload
Security Considerations
Port 465 provides encryption from the first byte, making it more secure than STARTTLS on port 587 which can be subject to downgrade attacks. Require strong authentication for all connections. Implement rate limiting to prevent spam. Use SPF, DKIM, and DMARC for email authentication. Monitor for suspicious sending patterns and compromised accounts.
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